1. Field of the Invention
This invention pertains to the field of instant coffee products. More particularly, the present invention is concerned with a process for collecting volatile aromatics liberated from roasted and ground coffee using gases which are present in the ground roast coffee and which act as a stripping medium and/or carrier for the volatile aromatics, and employing the collected volatile aromatics to make an instant coffee product having improved organoleptic properties.
2. Description of the Prior Art
The desirability of preparing an instant coffee product containing much of the aromatic materials originally contained within fresh roasted coffee beans, to provide an instant coffee having aroma and flavor comparable to fresh roasted coffee, has long been recognized.
According to one published source (Clifford, M. N., "The Composition of Green and Roasted Coffee Beans", Process Biochemistry, pp. 13-19, May 1975), taking fresh roasted coffee beans as containing 100% volatiles, during grinding of the roasted beans preliminary to the preparation of instant coffee a loss of about 14% of the volatiles is experienced. Further according to that source, during subsequent processing, i.e., extraction, concentration and drying, where no measures are taken to prevent the loss of volatiles, an additional 72% of the volatiles are lost. Thus, the final instant coffee retains a mere 14% of the original roast coffee volatiles.
Various expedients have been suggested in the prior art in an attempt to prevent the loss of volatile aromatics. Thus, techniques have been developed which, for example, are directed to recovering the volatiles evolved during the grinding of the roasted coffee beans. Other techniques have been proposed for preventing the loss of volatiles during subsequent processing steps. For example, aromatic constituents contained within the coffee extract may be removed and collected prior to concentration of the extract, e.g., stripping of the extract, and the removed volatiles may then be returned to the extract after it has been concentrated.
Various proposals have also been made to recover volatile aromatics which are normally lost during the extraction step, with which this invention is principally concerned. One such proposal, as disclosed in U.S. Pat. No. 2,432,759 issued to Heyman, for example, involves steam stripping volatile aromatics from a fresh extraction cell of roasted and ground coffee which has not been contacted with the extraction medium. After passing the steam through the extraction cell, the volatiles-laden steam is then passed through a number of condensers. Condensed volatile aromatics may then be added back to the concentrated extract.
That and similar techniques may suffer from a number of disadvantages. The extra time and expense required may be economically undesirable. Additionally, steam stripping unextracted ground roast coffee may subject the ground coffee to high temperatures which may cause some undesirable thermal degradation of its components.
In another technique involving recovery of volatile aromatics during the extraction step, steam is internally generated within the coffee extract as it leaves the final percolator. Such a technique is described, for example, in Canadian Pat. No. 1,001,476 issued to Bolt. In the Bolt technique, liquid coffee extract is first produced by a battery of percolators. The conditions in the Bolt process are such that steam is internally generated within the coffee extract as it leaves the final percolator. The extract at this point is at a temperature in the range of from about 100.degree. C. to 127.degree. C. The liquid extract is then passed through a separation chamber where flash evaporation of water and volatile aromatics takes place and where the aromatics-laden gases are separated from the liquid coffee extract. The volatile aromatics are then condensed and may be returned to the coffee extract either before or after that extract has been concentrated.
Although steam is internally generated within the coffee extract in the Bolt technique, in contrast to the technique described above wherein an external source of steam is provided for stripping, the Bolt process may nevertheless still suffer from a number of the same disadvantages discussed above. Thus, as in conventional steam stripping techniques, the employment of high temperatures for the internal generation of steam within the coffee extract may also cause some undesirable thermal degradation of its components.
Yet another technique involving the recovery of volatile aromatics during the extraction or percolation step (these terms conventionally being used interchangeably in the art) involves collecting volatile aromatics entrained with the gases that are evolved during the wetting of fresh roasted and ground coffee with an extraction medium.
In particular, as a result of roasting green coffee beans, carbon dioxide is produced; a substantial amount of which is occluded within the cells of the coffee even after the coffee beans have been ground. Additionally, air also fills the interstitial voids between the ground particles of coffee.
The first step in extraction is to wet the dry, fresh roasted and ground coffee with a hot extraction medium. As the extraction medium enters the bottom of a percolator in which the ground coffee is contained and begins to rise and fill the percolator, it gradually wets the roasted and ground coffee. While doing so, the extraction medium simultaneously displaces, with a "piston-like" effect, carbon dioxide, air and volatile aromatics which become entrained with these gases. For the sake of convenience and clarity, the term aromatics-laden gases will be used throughout this application to designate the mixture of carbon dioxide, air and any volatile aromatics that may be entrained with these gases.
During the wetting step, it is generally common to simply vent the aromatics-laden gases to the atmosphere as they are being evolved to prevent the possibility of the occurrence of undesirable foaming in the coffee extract.
At pages 297-300 of Volume 1 of "Coffee Processing Technology" by Sivetz, et al. (AVI, 1963), however, it is taught that there is a substantial amount of volatile aromatics entrained with the gases evolved during the wetting step of the percolator and that it is possible to recover these volatile aromatics by condensation.
Sivetz, et al. discloses taking the aromatics-laden gases evolved by the wetting step and passing them through a liquid-gas cyclone separator in which any extract that may have been carried over with the aromatics-laden gases from the extraction system is separated. The separated extract is then combined with unprocessed extract produced during subsequent extraction of the ground roast coffee. The separated aromatics-laden gases are then passed through an ice water chiller maintained at a temperature of 0.degree. C. with iced cooling water wherein most of the water, acetic acid and the least volatile aromatic components are condensed and then separated from the remaining aromatics-laden gases by subsequent passage through another liquid-gas cyclone separator. Sivetz, et al. teaches that this first condensate is also to be combined with unprocessed coffee extract. Finally, the balance of the aromatics-laden gases is then passed through a cold trap which is cooled by Freon-11 and dry ice to -73.33.degree. C. such that the aromatics-laden gases are cooled to -45.56.degree. C. This second condensate, according to Sivetz, et al. is also combined with unprocessed coffee extract.
The Sivetz technique too suffers from a number of disadvantages. Sivetz only treats the aromatics-laden gases that are evolved during the wetting phase of the extraction step and therefore only obtains volatile aromatics that are entrained with this portion of aromatics-laden gases. As will be discussed more fully hereinafter, applicant has discovered that additional aromatics-laden gases are present within the coffee extract itself which contains even more desirable fractions of volatile aromatics than those contained with the aromatics-laden gases evolved during the wetting phase of the extraction step. Sivetz has no appreciation or recognition of this. By treating only the aromatics-laden gases evolved during the wetting phase, Sivetz fails to collect the additional and more desirable volatile aromatics which are still contained within the coffee extract.
Moreover, by combining the first condensate with the unprocessed extract, Sivetz is uneconomically adding water back to the extract which subsequently will only have to be removed. Additionally, by combining the entire first condensate with the extract, Sivetz may also be adding the least volatile components to the extract among which are those which may have undesirable, harsh notes. Also contained within this first condensate are aromatic fractions which are relatively highly volatile. By Sivetz's prescribed teachings, these fractions too are combined with unprocessed coffee extract where they will most probably be lost during subsequent processing.
Finally, Sivetz's requirement that the second condensate be obtained by employing a cold trap maintained at a temperature of -73.33.degree. C. may also be undesirable. The refrigeration equipment involved is generally uneconomical and difficult to run due to ice formation. This second condensate may also contain undesirable aromatic fractions, particularly a -34.44.degree. C. fraction which has a distinct but objectionable sulfury note. Nevertheless, however, Sivetz teaches that the entire second condensate, which may also contain the undesirable -34.44.degree. C. fraction as well, is to be combined with the unprocessed extract.